DH is designed to be appealing to new players and easy to pick up, so DH tank should in theory be easy.
I had a very easy time getting into Prot Paladin though, personally. Easy AOE, defensive abilities felt natural to use, didn’t feel too different from playing melee DPS.
The hardest part about tanking is knowing the fights, not necessarily being amazing at your spec. If you know the fights I am sure you can pick up tanking pretty quickly on any of them.